Effect of low- and high-calcium dairy-based diets on macronutrient oxidation in humans

Objective: Higher calcium and dairy intakes may be associated with lower body weights, but a mechanism in humans has yet to be elucidated. We compared the effects of a dairy-based high-calcium diet and a low-calcium diet on macronutrient oxidation. Research Methods and Procedures: Subjects (10 men and nine women) consumed a low-dairy (LD, similar to one serving per day, similar to 500 mg Ca2+/d) or high-dairy (HD, similar to three to four servings per day, similar to 1400 mg Ca2+/d) energy balance diet for 1 week. Each diet condition was performed twice. On the 7th day, subjects were studied in a room calorimeter under one of four study conditions, applied in a randomized crossover design. Within each diet condition, subjects were studied under conditions of energy balance and acute energy deficit. The deficit (-600 kcal/d) was induced only for the 24 hours that subjects resided in the room and was achieved by a combination of caloric restriction and exercise. Results: Under energy balance conditions, there was no effect of diet treatment on respiratory quotient or 24-hour macronutrient oxidation. Under energy deficit conditions, 24-hour fat oxidation was significantly increased on the HD diet (HD with deficit=136 +/- 13 g/d, LD with deficit=106 +/- 7 g/d, p=0.02). Discussion: Consumption of a dairy-based high-calcium diet increased 24-hour fat oxidation under conditions of acute energy deficit. We hypothesize that these effects are due to an increased fat oxidation during exercise.